Image transfer process and also known as d/2888

ABSTRACT

A METHOD OF TRANSFERRING DIELECTRIC IMAGING MATERIAL CONTAINING A STATIC CHARGE FROM AN ELECTRICALLY CONDUCTIVE IMAGE BEARING SURFACE TO AN IMAGE RECEIVING SURFACE BY MEANS OF COULOMBIC ATTRACTION AND THE REARRANGEMENT OF ELECTRICAL CHARGES.

July 23, 1974 MENZ 3,825,423

IMAGE TR NSFER PROCESS AND ALSO KNOWN AS 13/2888 Original Filed Dec. 24, 1969 2 Sheets-Sheet .1

FIG. 2b

July 23, 1974 E, L, MENZ 3,825,423

IMAGE TRANSFER IROCESS"AND ALSO KNOWN AS .n/zaae Original Filed Dec. 24, 1969 2 Sheets-Sheet z nited States Patent US. Cl. 96-14 16 Claims ABSTRACT OF THE DISCLOSURE A method of transferring dielectric imaging material containing a static charge from an electrically conductive image bearing surface to an image receiving surface by means of coulombic attraction and the rearrangement of electrical charges.

This is a division, of application Ser. No. 887,805, filed Dec. 24, 1969 now U.'S. Patent 3,658,519.

BACKGROUND OF THE INVENTION The present invention relates in general to the transfer of images from an image bearing surface to an image receiving surface and more particularly to a method to accomplish such transfer by means of a rearrangement of static electric charges and coulombic attraction.

Various imaging processes are known wherein a thin film of material is deposited on a substrate or image bearing surface to provide a contrast to said surface in image configuration. Due to the process steps employed in producing such images, the substrate on which the image is first formed is, in some cases, not the substrate which is most durable, useful or desirable.

One such imaging process which provides images comprising a thin film or layer of an insulating or semi-conductive material on a substrate is the manifold imaging process as described in copending application Ser. No. 708,380, filed Feb. 26, 1968 now US. Pat. 3,707,368. In this imaging system, an imaging layer is prepared by coating a layer of electrically photosensitive imaging material onto a substrate. In one form the imaging layer comprises a photosensitive material such as metal-free phthalocyanine dispersed in a cohesively weak insulating or dielectric binder. This coated substrate is called the donor. When needed, the imaging layer is rendered cohesively weak. The process step of weakening the imaging layer is termed activation and in most cases the imaging layer is activated by contacting it with a swelling agent, solvent or partial solvent for the imaging layer or by heating the layer. A receiver sheet is laid over the surface of the imaging layer and an electric field is applied across the imaging layer while it is exposed to a pattern of light and shadow representative of the image to be reproduced. Upon separation of the donor substrate or sheet and receiving sheet, the imaging layer fractures along the lines defined by the pattern of light and shadow to which the imaging layer has been exposed. Part of the imaging layer is transferred to one of the sheets while the remainder is retained on the other sheet so that a positive image, that is, a duplicate of the original is produced on one sheet while a negative image is produced on the other.

In many instances, the apparatus employed to produce images by means of the manifold imaging process more conveniently uses donor and receiver sheets which are not well suited for the end use of the image. However, transferring images from one substrate to another Without loss of image quality has, in the past, been difiicult and required expensive and complicated machinery.

Patented July 23, 1974 SUMMARY OF THE INVENTION It is, accordingly, an object of this invention to provide a method for transferring an image from an electrically conductive substrate to another substrate which overcomes the above noted disadvantages.

Another object of this invention is to provide a method of transferring electrically insulating imaging material from an electrically conductive image bearing surface to an image receiving surface without complex equipment.

Another object of this invention is to provide images of improved quality which have been transferred from an image bearing substrate to an image receiving medium.

These and other objects of this invention are apparent from the following description of the invention.

In accordance with this invention, there is provided a process whereby a releasable image residing on an electrically conductive image bearing medium is transferred to an image receiving medium. Such transfer is accomplished by placing an electric charge of known polarity on the surface of the material which forms the image and then sandwiching the charged imaging material between the image bearing medium and an image receiving medium thus forming an image transfer set. An electric field is then established across the image material and image receiving medium which field is supplied by a static charge in an insulating layer. When the polarity of the electric field across the image material is adjusted properly, the image material adheres to the image receiving medium. Upon separation of the sandwich or set, there is provided a high quality image on the image receiving substrate.

According to this invention, the image material and a separate layer is electrically charged and such charge is held until after the transfer is accomplished. Thus, the process of this invention is particularly adapted for use in transferring images wherein the image material is electrically insulating and which maintains electric charge for at least a brief period of time. A wide variety of materials can thus be employed as the image material and the charged layer in the process of this invention. Insulating materials such as polyethylene, polypropylene, polyamides, polymethacrylates, polyacrylates, polyvinylchlorides, polyvinylacetates, polystyrene, polythioloxanes, chlorinated rubber, polyacrylonitrile, epoxies, phenolics, hydrocarbon resins and other natural resins such as rosin derivatives as well as mixtures and copolymers of the above materials can be employed. Particularly preferred images to be transferred according to the process of this invention are those comprising insulating materials which retain a charge and which are or can be rendered releasable. Such materials include microcrystalline waxes such as: Sunoco 1290, Sunoco 5825, Sunoco 985, all available from Sun Oil Co.; Parafiint RG, available from the Moore and Munger Company; paraflin waxes such as: Sunoco 5512, Sunoco 3425, available from Sun Oil Co., Sohio Parowax, available from Standard Oil of Ohio; waxes made from hydrogenated oils such as: Capitol City 1380 wax, available from Capitol City Products, Co., Columbus, Ohio; Caster Wax L-2790, available from Baker Caster Oil Co.; Vitikote L-340, available from Duro Commodities; polyethylenes such as: Polyethylene DYIT, Polyethylene DYLT, Polyethylene DYDT, all available from Union Carbide, Corp; Marlex TR 822, Marlex 1478, available from Phillips Petroleum Co.; Epolene C-13, Epolene C-lO, available from Eastman Chemical Products Co.; Polyethylene AC6, Polyethylene AC612, Polyethylene AC324, available from Allied Chemicals; modified styrenes such as: Piccotex 75, Piccotex 100, Piccotex 120, available from Pennsylvania Industrial Chemical; Vinylacetate-ethylene copolymers such as: Elvax Resin 210, Elvax Resin 310, Elvax Resin 420, available from E. I. du Pont de Nemours Co., Inc., Vistanex MH, Vistanex L-80, available from Enjay Chemical Co.; vinyl chloridevinyl acetate copolymers such as: Vinylite VYLF, available from Union Carbide Corp.; styrene-vinyl toluene copolymers; polypropylenes; and mixtures thereof.

There has recently been discovered a photoelectrophoretic imaging method wherein electrically photosensitive pigments are employed to produce images under the influence of light and an electrical field. Images made by this process comprise individual particles of electrically photosensitive materials which are capable of retaining an electric charge. Such a process is more fully described in US. Pat. 3,384,565 which is incorporated herein by reference. Images produced in accordance with the process described in the patent can be transferred by the method of this invention. The materials employed to produce images by means of the manifold imaging process are more fully described in copending application Ser. No. 708,380 filed Feb. 8, 1969, which description is incorporated herein by reference. Both of the above mentioned imaging processes employ electrically photosensitive materials which are also a dielectric material capable of retaining a charge. Thus, images produced by such processes may be transferred from an image bearing medium to an image receiving medium in accordance with the process of this invention. On the other hand, dielectric imaging materials which do not contain electrically photosensitive materials may also be transferred in accordance with this invention.

Where the image material is not releasable from the image bearing medium to allow irnagewise transfer, it is desirable to include an activation step in the process of this invention. The activation step may take many forms such as heating the imaging layer thus reducing the adhesive strength or applying a substance to the surface of the imaging material or including a substance in the imaging material which substance lowers the adhesive strength of the imaging material with respect to the image bearing medium. The substance so employed is termed an activator. Preferably, the activator should have a high resistivity so as to prevent electrical breakdown of the transfer set. Accordingly, it will generally be found to be desirable to purify commercial grades of activators so as to remove impurities which might impart a higher level of conductivity. This may be accomplished by running the fluids through a clay column or by employing any other suitable purification technique. Generally speaking, the activator may consist of any suitable material having the aforementioned properties. For purposes of this specification and the appended claims, the term activator shall be understood to include not only materials which are conventionally termed solvents but also those which are partial solvents, swelling agents or softening agents for the imaging material. The activator can be applied at any convenient point in the process prior to separation of the sandwich.

It is generally preferable that the activator have a relatively low boiling point so that fixing of the image on the image receiving medium can be accomplished upon evaporation of the activator. It is desirable that fixing of the image be accomplished quickly with mild heating at most. It is to be understood, however, that the invention is not limited to the use of these relatively volatile activators. In fact, very high boiling point non-volative activators including silicone oils such as dimethyl-polysiloxanes and very high boiling point long chain aliphatic hydrocarbon oils ordinarily used as transformer oils such as Wemco-C transformer oil, available from Westinghouse Electric Co., have also been successfully utilized in the imaging process. Although these less volatile activators do not dry off by evaporation, image fixing can be accomplished by contacting the image with an absorbent sheet such as paper which absorbs the activator fluid. In short, any suitable volatile or non-volatile activator may be employed. Typical activators include Sohio Odorless Solvent 3440, an aliphatic (kerosene) hydrocarbon fraction, available from Standard Oil Co. of Ohio, carbon tetrachloride, petroleum ether, Freon 214 (tetrafiuoro-tetrachloropropane), other halogenated perchloroethylene, trichloromonofluoromethane, trichlorotrifiuoroethane, trichlorotrifluoroethane, ethers such as diethyl ether, diisopropyl ether, dioxane, tetrahydrofuran, ethyleneglycol monoethyl ether, aromatic and aliphatic hydrocarbons such as benzene, toluene, xylene, hexane, cyclohexane, gasoline, mineral spirits and white mineral oil, vegetable oils such as coconut oil, babussu oil, palm oil, olive oil, castor oil, peanut oil and neatsfoot oil, decane, dodecane and mixtures thereof. Sohio Odorless Solvent 3440 is preferred because it is odorless, nontoxic and has a relatively high flash point.

The image receiving medium useful in the process of this invention may comprise any suitable electrically insulating or electrically conducting material. Insulating materials are preferred since they can be employed in a double function of the process of this invention. That is, an electrically insulating image receiving medium containing a static electric charge can also be employed to provide the electric field required to transfer the imaging material to the image receiving medium. Typical insulating materials include polyethylene, polypropylene, polyethylene terephthalate, cellulose acetate, paper, plastic coated paper such as polyethylene coated paper, vinyl chloridevinylidene chloride copolymers and mixtures thereof. Mylar (a polyester formed by the condensation reaction between ethylene glycol and terephthalic acid available from E. I. duPont de Nemours & Co., Inc.) is preferred because of its durability and excellent insulative properties.

According to the process of this invention, the image material and an image receiving medium are subjected to electrical fields. The electrical fields in the form of static charges in an insulating or dielectric material can be applied in many ways. Static electrical charges can be imposed on an insulating layer which layer is then incorporated into the transfer set. For example, is those instances wherein the image receiving medium is an electrically insulating material, the image receiving medium may receive an electric charge on each surface. The electrical fields are established across the imaging material and image receiving medium by backing the image receiving medium with an electrically conductive layer and connecting the conductive layer to a similarly conductive layer upon which the image resides. The sandwich is then separated during or after the two conductive layers are electrically inter-connected. A separate dielectric layer can be electrically charged and employed as a backing on the image bearing medium. A conductive layer is then employed as a backing for the charged dielectric layer and electrically interconnected to a conductive layer acting as a backing for the image receiving medium. The sandwich is then separated while the conductive layers are electrically connected. Other configurations are described below while still others will occur to those skilled in the art.

Static charges can be imposed upon dielectric layers by means known to the art as by contacting the layer with an electrically charged electrode. Alternatively, the layer may be charged using corona discharge devices such as those described in US. Pat. No. 2,588,699 to Carlson, US. Pat. 2,777,957 to Walkup, US. Pat. 2,885,556 to Gundlach or by using conductive rollers as described in US. Pat. 2,980,834 to Tregay et al. or by frictional means as described in US. Pat. 2,297,691 to Carlson or other suitable apparatus.

Thus, electrical fields across the imaging material and image receiving medium are provided by communicating static charges from one side of the transfer set to the other side. To extend the fields electrically conductive layers are employed. The conductive layers employed may comprise any suitable conductive material and may be flexible or rigid. Typical conductive materials include metals such as aluminum, brass, steel, copper, nickel, zinc etc. Also, metallic coatings on plastic substrates, rubber rendered conductive by the inclusion of a suitable material therein and the like can be employed. Conductive rubber is preferred because of its flexibility. Transparent conductive electrodes such as tin oxide coated glass may be employed but are not required as the transfer of the image can take place in the dark. Such conductive materials can also be employed as the image bearing medium. I

The surface of the insulating image material and the insulating layer are electrically charged to the extent required to transfer the image. The amount of charge will vary depending in part upon the dielectric constant, polarity of the charge and thickness of the image material. It will also vary depending upon the dielectric constant and thickness of the insulating material in the transfer set. When employing a material exhibiting an extremely high dielectric constant, lower voltages can be employed such as from about 200 to about 400 volts. Alternatively, if materials exhibiting very low dielectric constant are employed, higher voltages are employed ranging up to an amount less than the electrical breakdown strength of the image bearing medium.

In general, the transfer voltage is calculated according to the following formula:

where V =a constant for the image material K =dielectric constant of the image material K =dielectric constant of the insulating image receiving medium D =thickness of insulating image receiving medium D =thickness of insulating image material In a case wherein the insulating image receiving medium is 1 mil in thickness and has a dielectric constant of 3.25, and the image material is .2 mil having a dielectric constant of 5, the calculated transfer voltage is two thousand volts where the image material constant is 240 and the image receiving medium is also the charged insulating layer.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages of this improved method of transferring images will become apparent upon consideration of the detailed disclosure of the invention especially when taken in conjunction with the accompanying drawings wherein:

FIG. 1a illustrates another image transfer sandwich prior to communicating an electric field across the imaging material.

"FIG. 1b illustrates an image transfer sandwich after the communication of an electric field across the imaging material and separation of the sandwich resulting in the transfer of the imaging materials.

FIGS. 2a and 2b are side sectional views of another image transfer sandwich before and after the imaging material is subjected to an electric field and partial separation of the sandwich.

FIG. 3 illustrates an apparatus for carrying out a process of the invention in an automatic and continuous mode of operation.

DETAILED DESCRIPTION OF THE DRAWINGS FIGS. 1a and 2b illustrate an embodiment of this invention wherein releasable imaging material 21 is transferred from electrically conductive image bearing medium 23 to an insulating image receiving medium 25. In FIG. la, an expanded view, image receiving medium 25 comprises an insulating material which has been electrically charged on the surface and positioned under flexible electrode 27 so that the side facing the charged imaging material 21 is of opposite polarity to the charge on the imaging material. In this embodiment no switching means are required provided that electrode 27 is not laid over to image receiving medium 25 until image transfer is desired. PIG. lb, wherein the numerals are as indicated for FIG. la, illustrates the transfer of imaging material 21 from conductive image bearing medium 23 to the charged dielectric image receiving medium 25 upon separation of the image transfer sandwich. Flexible electrode 27 is laid over image receiving medium 25 and by means of electrically conductive wire 27a connected to image bearing medium 23, the charge in image receiving medium 25 supplies an electric field across the imaging layer. Alternatively, an uncharged conductive or insulating image receiving medium 26 can be inserted between the charged insulating material 25 and imaging material 21 whereupon, as shown in FIG. lb imaging material 21 adheres to image receiving medium 26 upon separation of the set.

FIGS. 2a and 2b illustrate another embodiment of an image transfer sandwich wherein electrically charged releasable imaging material 31 is transferred from electrically conductive image bearing medium 33 to an ordinary uncharged paper image receiving medium 35. The electric field is provided by means of a layer of insulating material 37 which has been electrically charged on each surface and positioned in the transfer sandwich so that the polarity of the surface of the insulating layer which is the same as the charged image material 31 is contacting conductive image bearing medium 33. Conductive layer 39 resting on the charged dielectric layer 37 and conductive layer 41 provide the means by which the imaging layer is subjected to an electric field when conductive wire 43 is connected to both conductive layers. Control of the electric field to be provided by the static charge and dielectric layer 37 is achieved without switching means by preventing the electrical connection between conductive layer 39 and conductive layer 41 prior to when image transfer is desired. Such connection can be made by providing a conductive clamp on the loose end of wire 43. Referring now to FIG. 2b, there is illustrated the transfer of imaging material 31 from conductive image bearing medium 33 to image receiving medium 35 after wire 43 is connected to conductive layer 41. The transfer image is exposed to view upon separation of the sandwich.

The embodiments of this invention illustrated in FIGS. 1 and 2 described above, are representative of the various configurations of the image transfer set of this invention. Such embodiments as illustrated may be performed manually or be adapted for machine use. The method of this invention is advantageously employed in an apparatus which carries out the process of the invention in an automatic and continuous mode of operation. While not intending to limit the scope of this invention, FIGS. 4 and 5 describe some of the preferred embodiments of this invention.

Referring now to FIG. 3 there is shown a continuous process for transferring an image from an image bearing medium to an image receiving medium in accordance with the process of this invention. Imaging material 45 releasably residing on image bearing medium 47 which is electrically conductive is first charged by passing it over a corona discharge device 49 which is connected to an 8,000 volt D.C. source of potential 51. After being charged, imaging material 45 is brought into contact with insulating image receiving material 55. The image transfer set then passes between conductive roller 57 and an electrically charged insulating web 59. Insulating web 59 is entrained over conductive roller 61 and 62. The electrically insulating web 59 is electrically charged by contacting a corona discharge device 63 which alternatively can be a charge bearing roller. Corona 63 is connected to a 10,000 volt power supply 64. Conductive roller 61 and the conductive roller 57 are connected by wire 58 so as to establish an electric field across the imaging material by utilizing the static charge in electrically insulating web 59. The polartiy of the charge on imaging material 45 and the charge on the electrically insulating portion of web 59 are coordinated so as to place a charge on conductive roller 57 opposite in polarity to the charge on imaging material 45. After passing between roller 57 and web 59, the image transfer sandwich is separated and imaging material 45 adheres to image receiving medium 55. If necessary, prior to combining the image bearing medium and image receiving medium into the image transfer set, an activator may be applied to imaging material 45 so as to render the material releasable from image bearing medium 47. A liquid activator can also be applied to image receiving medium 55 prior to incorporating it into the image transfer set. In addition and in those instances wherein heat may act as an activator, a pair of heating rollers may be added to the system.

The process of this invention is particularly useful in transferring images which have been produced by means of the manifold imaging process referred to above. Images produced by the manifold process comprise insulating materials which retain a residual electrical charge that is acquired during the production of the image. Thus, images produced by means of a manifold imaging process are readily useful in the process of this invention.

In accordance with the process of this invention, images can be transferred to a wide variety of image receiving media. For example, images can be transferred to cloth, drafting film, vellum, ordinary paper, leather, thermoplastic materials, photographic film, metals such as iron, silver, aluminum, tin, etc. In addition, images can be transferred in accordance with the process of this invention to irregular surfaces which would be unusable in the process by which the original image is formed. That is, in one or more of the process steps by which the image is originally formed, smooth surfaces are required least incomplete processing occur on an irregular surface. However, as will be seen in the following examples, many different types of surfaces may be employed as the image receiving medium in the process of this invention. In addition, highly useful image receiving media can be employed such as metal or plastic lithographic plates. Surprisingly, high quality prints can be prepared from lithographic plates made from images transferred in accordance with the process of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following examples further specifically illustrate the present invention. The examples below are intended to illustrate various preferred embodiments of the image transfer process of this invention. The parts and percentages are by weight unless otherwise indicated.

EXAMPLE I An image is produced by means of a manifold imaging process as described in Example XXVIII of copending application Ser. No. 708,380 filed Feb. 26, 1968 while employing aluminum foil as the receiver and a sheet of 2 mil thick Mylar as a donor. After image exposure, the polarity of the electrodes is reversed. Upon separation of the donor and receiver a positive image resides on the aluminum foil having a negative electrical charge. The positive image residing on the aluminum foil is then placed face down upon a paper lithographic plate which is resting upon an aluminum plate. A sheet of 3 mil polystyrene is electrically charged by passing the sheet between a pair of rollers attached to a 10,000 volt DC. power supply which places a negative charge on one side of the sheet and a positive charge on the other side. The charged polystyrene sheet is then laid on the back of the aluminum image bearing medium with the negatively charged side of the polystyrene facing the aluminum. A conductive rubber electrode is then laid on the positively charged side of the polystyrene sheet and is connected by means of a copper wire to a metal plate upon which the paper lithographic plate resides. Immediately after the connection is made, the aluminum foil together with the charged polystyrene sheet and black rubber electrode is pulled away from the lithographic plate leaving a right reading good quality image on the lithographic plate. The image is then fixed by heating slightly to remove residual activators left from the manifold imaging process.

The lithographic plate so prepared is employed in a lithographic printing operation using oil based ink to produce printed copies of the image and over 5,000 good quality printed copies of the image are produced.

EXAMPLE II An image is first prepared by means of the photoelectrophoretic color imaging process as described in U.S. Patent 3,384,565 by coating an 8% by weight suspension including equal amounts of the following pigments: Watchung Red B, a barium salt of 1-(4-methyl-5'-chloroazobenzene-2-sulphonic acid)-2-hydroxy-3-naphthoic acid C. I. No. 15865; Monolite Fast Blue GS, the alpha form of metal-free phthalocyanine, C. I. No. 741 00; and l-cyano- 2,3-phthaloyl-7,8 benzopyrrocoline as synthesized according to the first technique given for its synthesis on page 1215 of the Mar. 5, 1957 edition of the Journal of the American Chemical Society in an article entitled Reactions of Naphthoquinones with Malonic Ester and its Analogs III l-substituted Phthaloyl and Phthaloyl Benzopyrrocolines by Pratt et al. These pigments are magenta, cyan and yellow respectively. This mixture, which shall be referred to as a trimix hereinafter, is subjected to an electric field by connecting the conductive surface of the glass plate in series with the switch, a potential surface and a conductive center of a roller having a coating of baryta paper on its surface. The roller is approximately 2 /2 inches in diameter. A full color positive photographic transparency is projected through the glass plate onto the trimix by placing the transparency between the suspension and a white light source as the roller is moved across the surface of the coated glass plate. The roller is held at a negative potential of 2,500 volts with respect to the conductive glass plate. The roller is passed over the glass plate 3 times and cleaned after each pass. After completion of 3 passes, it was found that an excellent quality full color image with all colors well separated was left behind on the glass plate. The electric field and exposure were both continued during the entire period of the six passes by the roller. After discontinuing the voltage on the NESA, a sheet of bond paper wetted with kerosene is laid over the image which is residing on the conductive surface of the glass plate. A sheet of polystyrene which has been charged by passing the sheets between a pair of rollers connected to a 8,000 volt DC. power supply is laid over the paper with the positively charged side of the polystyrene sheet against the paper. A black rubber electrode is placed over the charged styrene and is connected to the conductive surface of the glass plate and immediately after making the connection the paper, charged styrene sheet and black rubber electrode are removed from the glass plate. The image which was formerly residing upon the glass plate adheres to the bond paper and is fixed by applicaton of a transparent polymer coating.

EXAMPLE III is electrically interconnected with the aluminum sheet under the polystyrene by means of a 14 gauge copper wire. The image bearing medium is then separated from the bond paper leaving the image adhering to the paper.

EXAMPLE IV A positive and negative copy of an image are prepared by means of the manifold imaging process according to the procedure of Example I with the exception that both the donor and receiver are electrically conductive. While the imaging material of each copy retains an electric charge and are releasable, the images are brought together in register but inserted between them is a 1 mil sheet of Mylar. A 2 mil sheet of polystyrene carrying a charge of 4,000 volts is placed against the donor with the positively charged side in contact. The polystyrene is laid upon an aluminum sheet and an electrical connection is made between the aluminum sheet and the conductive medium bearing the receiver image. When voltage equilibrium across the set is attained, the donor and receiver are separated. The image formerly residing on the donor now adheres to the 1 mil Mylar sheet inserted between the donor and receiver and on the other side of the 1 mil Mylar sheet there is found an image which formerly resided on the receiver. This is, thus, produced a 1 mil Mylar sheet having on its respective side a negative and positive image of the same original which images are in register with each other.

EXAMPLE V The following example illustrates the use of the present image transfer method to provide a novel means for proofing color separations of a color original image. Three donors are made according to the procedure of Example I with a different electrically photosensitive material in each imaging layer. The materials employed are metalfree phthalocyanine, a cyan color, Algol Yellow GC and the magenta color 2,9-dimethylquinacridone. Three different manifold sets are then prepared by combining an aluminum foil receiver sheet with each of the yellow, cyan and magenta donors. In accordance with the procedure of Example I, the yellow, cyan and magenta manifold sets are exposed through a screen to blue, red and green color separations, respectively, formed from a colored original. After separation of the manifold sets under a field, the positive images residing on the receiver are superimposed by transfer upon one sheet of non-conductive paper in accordance with the transfer procedure of Example I. The first positive image transferred to the paper is the yellow followed by the magenta and finally the cyan positive image on the top so that a screened proof of the original colored image is provided. At the same time, the three screened negative images formed upon separation of the manifold sets are ready for use in making the plate providing the proof is satisfactory. It is accordingly seen that the proof of a full-color image can be provided on an opaque substrate which can be viewed directly. Alternatively, all three positive or negative images could be transferred to a transparent substrate. A black separation could also be provided by imaging a black separation on a donor prepared as described in Example VI and superimposing the positive black manifold image on the same substrate as the other three images.

In all of the above Examples, a right reading copy is obtained by the process of this invention by employing when necessary an appropriate number of mirrors in the optical system employed to produce the image. The use of mirrors in producing the image will provide a compensating factor which produces a right reading positive image when transferred in accordance with the process of this invention.

Although specific components and proportions have been stated in the above description of the preferred embodiments of the invention, other typical materials as listed above, if suitable, may be used with similar results.

Other modifications and ramifications of the present invention will occur to those skilled in the art upon a reading of the present disclosure. These are intended to be included within the scope of this invention.

What is claimed is:

1. A method of transferring a releasable insulating image from a conductive image bearing medium to an image receiving medium comprising:

(a) electrically charging said imaging material to a known polarity and electrically charging the surface of an insulating layer to an image transfer voltage;

-(b) contacting said charged image with said image receiving medium;

(c) electrically connecting said image bearing medium to the surface of said insulating layer said surface having the same charge polarity as said image and electrically connecting the other surface of said insulating layer to said image receiving medium whereby said image adheres to said receiving medium; and

(d) separating said image bearing medium from said image receiving medium thereby transferring said image from said conductive medium to said receiving medium.

2. The method of Claim 1 further including the step of rendering said image releasable by applying thereto an activator to said imaging material.

h 3. The method of Claim 2 wherein the activator is eat.

4. The method of Claim 1 wherein the insulating layer is a thermoplastic material.

5. The method of Claim 1 wherein the image receiving medium is electrically conductive.

6. The method of Claim 1 wherein the image receiving medium is the charged insulating layer.

7. The method of Claim 1 wherein the insulating layer comprises polystyrene.

8. The method of Claim 1 wherein the imaging material comprises an electrically photosensitive material dispersed in an insulating binder.

9. The method of Claim 1 wherein the imaging material is an electrically photosensitive materia.

10. The method of Claim 1 wherein said electric charge on said insulating layer is in the range of from about 1,000 volts per mil to about 7,000 volts per mil. I 11. The method of transferring a releasable insulating lmaging material from an electrically conductive image bearing medium to an image receiving medium comprising the steps of:

(a) providing an electrically charged imaging material of a known polarity;

(b) contacting said charged imaging material with an image receiving medium having an electrically charged insulating layer as a backing with said layer positioned such that the side contacting said image receiving medium is of opposite polarity to the charged imaging material;

(c) contacting said charged insulating layer on its side opposite said receiving medium with an electrically conductive layer;

(d) electrically interconnecting said conductive layer and said image bearing medium and separating said image bearing medium from said image receiving medium, thereby transferring said image from said image bearing medium to said receiving medium.

12. The method of Claim 11 wherein the electric charge in said charge dielectric layer is in the range of from 1,000 volts to about 9,000 volts per mil.

13. The method of Claim 11 wherein said imaging material is an organic electrically photosensitive material.

14. The method of Claim 11 wherein said image material comprises an electrically photosensitive material dispersed in an insulating material binder.

15. The method of Claim 14 wherein said electrically photosensitive material is an organic material.

1 1 I 1 2 16. The method of transferring the photographically a field across said sandwich by means of electrically positive and negative images of an original, which images colldllctlv'e comprise releasable electrically charged insulating imaging Separatlng Sald SaIldWlch wh r by each Image adheres to the image receiving media when voltage material residin on electricall conductive ima e bearin g y g g equilibnum across the sandwlch 1s achieved.

media to the opposite sides of a single substrate comprising the steps of References Cited (a) provlding an insulating layer contammg a static UNITED STATES PATENTS electric charge;

(b) sandwiching a single image reeciving media be- 10 g a 7 5 d en tween each of 531d charge Images 3,512,768 5 9 0 Tulagin 9 1 2 (c) subjecting said sandwich to an electric 'field wherein the image bearing media is at the same polarity as CHARLES VAN HORN, Primary Examiner said charged imaging material which it bears, by positioning said charged insulating layer in contact 15 US. Cl. X.R. with one of said image bearing media and extending 96-1 R; 11737 R 

